An autostereoscopic display device refers to a display device with which an image with stereoscopic effect can be observed through naked eyes without wearing glasses. A slit grating type autostereoscopic display device can alternately display pixels of a display panel by column as left parallax images and right parallax images, and a grating is provided in front of or behind the display panel in parallel. In a basic structure as shown in FIG. 1, gratings 101 are parallel provided in front of display panel 100. With the shielding effect of the gratings, the left eye and right eye of an observer see left parallax images and right parallax images displayed by pixels on a display panel, respectively, and thus the observer obtains a visual stereoscopic display image. The core component of a slit grating type autostereoscopic display device is grating. In prior art, lens grating and slit grating are the two main techniques. Wherein, slit grating can further be divided into black-and-white stripe slit grating and liquid crystal slit grating. Liquid crystal slit grating can be used not only for stereoscopic display, but also for switching between two-dimensional display and three-dimensional display.
Liquid crystal slit grating (i.e., a liquid crystal cell which can form slit grating) includes twisted nematic liquid crystal mode (abbreviated as TN mode) liquid crystal slit grating, advanced super dimension switch (abbreviated as ADSDS mode) liquid crystal slit grating, and the like. Wherein, TN mode liquid crystal slit grating is a liquid crystal slit grating whose liquid crystal molecular forms a nematic liquid crystal layer with twisted angle of 90 degree, and ADSDS mode liquid crystal slit grating is a liquid crystal slit grating of which all oriented liquid crystal molecular between and right above the slit electrodes in a liquid crystal cell can be rotated through multiple dimension electric field, and the multiple dimension electric filed consists of the electric field generated by the edges of the slit electrodes in the same plane and the electric field generated between a slit electrode layer and a plate electrode layer.
As shown in FIG. 2, an existing TN mode liquid crystal slit grating 200 includes a first grating substrate and a second grating substrate. Nematic liquid crystal layer 230 with twisted angle of 90 degree is provided between the first grating substrate and the second grating substrate. The first grating substrate includes a first polarizer 213, a first substrate 210, a first electrode 211 covering the first substrate 210 and a first alignment layer 212 covering the first electrode 211. The second grating substrate includes a second polarizer 223, a second substrate 220, a second electrode 221 including a plurality of stripe electrodes parallel to each other and a second alignment layer 222 covering each stripe electrode and interval areas between the stripe electrodes.
In a case where the polarization directions of the first polarizer 213 and the second polarizer 223 are perpendicular to each other (i.e., the liquid crystal slit grating 200 is normally white mode), when there is no potential difference between the first electrode 211 and the second electrode 221, the nematic liquid crystal layer 230 provided between the first grating substrate and the second grating substrate twists the polarization direction of light by 90 degree, and thus light can pass through the first polarizer 213 and the second polarizer 223. In other words, when there is no potential difference between the first electrode 211 and the second electrode 221, the liquid crystal slit grating 200 wholly is transparent, and thus can be used for two-dimensional display. On the other hand, when an operating potential difference exists between the first electrode 211 and the second electrode 221, the potential difference cause the nematic liquid crystal layer 230 located between each stripe electrode of the second electrode 221 and the first electrode 211 not to twist the polarization direction of light by 90 degree, thus the liquid crystal slit grating 200 displays black stripes at the position of each stripe electrode, and transparent white stripes are formed between adjacent black stripes. A plurality of black stripes form opaque stripe area, and a plurality of white stripes form transparent stripe area. Consequently, the liquid crystal slit grating 200 becomes a slit grating with black stripes and white stripes at intervals, and can realize three-dimensional display working with a display panel.
In a case where the polarization directions of the first polarizer 213 and the second polarizer 223 are parallel to each other (i.e., the liquid crystal slit grating 200 is normally black mode), when there is no potential difference between the first electrode 211 and the second electrode 221, the nematic liquid crystal layer 230 provided between the first grating substrate and the second grating substrate twists the polarization direction of light by 90 degree, and thus the light cannot pass the second polarizer 223 after passing the first polarizer 213. In other words, when there is no potential difference between the first electrode 211 and the second electrode 221, the liquid crystal slit grating 200 wholly is opaque. On the other hand, when an operating potential difference exists between the first electrode 211 and the second electrode 221, the operating potential difference cause the nematic liquid crystal layer 230 located between each stripe electrode of the second electrode 221 and the first electrode 211 not to twist the polarization direction of light by 90 degree any longer, thus the liquid crystal slit grating 200 displays white stripes at the position of each stripe electrode, and opaque black stripes are formed between adjacent white stripes. A plurality of black stripes form opaque stripe area, and a plurality of white stripes form transparent stripe area. Consequently, the liquid crystal slit grating 200 becomes a slit grating with spaced black stripes and white stripes, and can realize three-dimensional display working with a display panel.
In prior art, TN mode liquid crystal slit grating mostly uses ball spacers to support the first grating substrate and the second grating substrate. As ball spacers are disposed by way of spraying, a lot of ball spacers are sprayed in opaque stripe area and a lot of ball spacers are sprayed in transparent stripe area at the same time, and the location of a ball spacer cannot be accurately controlled. A ball spacer is isotropic and does not twist the polarization direction of light. For liquid crystal slit grating in normally white mode (i.e., the polarization directions of the first polarizer 213 and the second polarizer 223 are perpendicular to each other), the ball spacers located in the transparent stripe area may form black dots in the transparent stripe area, and thus affecting light transmittance. Therefore, for liquid crystal slit grating in normally white mode, the formation manner of the ball spacers will cause that the location of each ball spacer cannot be accurately controlled, and further the effect of the ball spacers on light transmittance cannot be accurately controlled. On the other hand, for liquid crystal slit grating in normally black mode (i.e., the polarization directions of the first polarizer 213 and the second polarizer 223 are parallel to each other), the ball spacers located in the opaque stripe area may form white dots in the opaque stripe area, and thus being displayed as light leak and causing crosstalk, as shown in FIG. 3. Therefore, for liquid crystal slit grating in normally black mode, the formation manner of the ball spacers will cause that the locations of ball spacers cannot be accurately controlled, and further crosstalk caused by the ball spacers cannot be accurately controlled.
The above problems exist not only in a TN mode liquid crystal slit grating, but also in a liquid crystal slit grating of other mode, such as a ADSDS mode liquid crystal slit grating.